Food-grade strategies to increase stability of whey protein particles: Particle hardening through aldehyde treatment

Abstract

Protein particles are promising systems for encapsulation purposes and structure building and stabilization in a food context (Arroyo-Maya & McClements, 2015; Oduse, Campbell, Lonchamp, & Euston, 2017). Whey protein isolate (WPI) nanoparticles can be easily produced using liquid antisolvent precipitation. An additional particle hardening step is however often required, since WPI particles tend to disintegrate in aqueous environment. In this study, the potential of different food-grade aldehydes (i.e. cinnamaldehyde, salicylaldehyde, syringaldehyde, vanillin and p-anisaldehyde) to stabilize the protein particle matrix was explored. In general, the largest increase in stability against disintegration was observed for vanillin-treated particles. Incubation with vanillin did not only improve particle stability in aqueous environment, but also during isothermal storage (T = 6, 23 or 37°C for 3 weeks) and thermal treatment (T ≤ 80°C for 30 min). Although less pronounced, an increased particle stability in aqueous environment was also observed after salicylaldehyde or syringaldehyde treatment. All particles however disintegrated at pH values far removed from their isoelectric point (IEP ≈ pH 4.9), while extensive aggregation was observed near the IEP and under variable salt concentrations (0-250 mM NaCl). Vanillin treatment did not induce conformational changes or covalent bond formation within the particle matrix. Therefore, the observed hardening effect presumably results from non-covalent interactions between vanillin and protein molecules. The provided insights will serve as a basis to further optimize the stabilization of protein-based systems, with the eventual goal of increasing their application potential in the food industry.

Heat treatment as a food-grade strategy to increase the stability of whey protein particles under food system relevant conditions

“…Suspensions of protein NPs in 80.8 v/v% aqueous ethanol were fabricated using an optimized LAS method, as described by Boeve & Joye (2020). In short, 2.0 w/v% protein (WPI, β-Lg, α-La, BSA) was dissolved in distilled water and stirred for at least 1 hour.…”

“…The particle size distributions and polydispersity indices (PDI) of the control and heat pretreated WPI particle suspensions were determined with dynamic light scattering (Zetasizer Nano ZS, Malvern Instruments Ltd., Worcestershire, UK), as in Boeve & Joye (2020. The ZP values of the WPI NPs were measured using particle electrophoresis (Zetasizer Nano ZS, Malvern Instruments Ltd., UK).…”

“…In a similar approach as that described in Boeve & Joye (2020), untreated and heat pretreated WPI NP suspensions (Section 2.2) were diluted 10 times with distilled water to reduce the ethanol concentration from 80.8 v/v% (undiluted suspensions) to 8.1 v/v% (diluted suspensions), after which the samples were briefly stirred prior to being incubated for 24 hours at RT. The particle size (distribution), mean diameter, PDI and ZP were analyzed as in section 2.3 before as well as after sample dilution and changes in these parameter values were used to evaluate particle stability.…”

“…The method relies on the tendency of protein molecules to interact and aggregate, likely after (partial) denaturation, in a controlled way as the solvent quality of the medium decreases. For research purposes, LAS has already been successfully used to fabricate food-grade NPs from, amongst others, whey proteins (Bagheri et al, 2013;Boeve and Joye, 2020). Most often, the antisolvent for the production of whey protein isolate (WPI) based NP production using LAS, is ethanol.…”

“…For the second type of destabilization, an additional particle hardening step is often required, since WPI NPs tend to disintegrate in aqueous environment. In previous research by our group, aldehyde treatments have been explored as a possible food-grade strategy to increase the stability of LAS-produced WPI NPs in an aqueous environment (Boeve and Joye, 2020). Vanillin was found to hold the greatest potential as a food-grade particle stabilizer, significantly increasing resistance against particle disintegration in an aqueous environment, even at elevated temperatures.…”